U.S. patent number 4,692,335 [Application Number 06/771,868] was granted by the patent office on 1987-09-08 for calcium hypochlorite tablet.
This patent grant is currently assigned to PPG Industries, Inc.. Invention is credited to Donald P. Iwanski.
United States Patent |
4,692,335 |
Iwanski |
September 8, 1987 |
Calcium hypochlorite tablet
Abstract
Novel solid articles comprising a compressed mixture of granular
calcium hypochlorite and from about 0.5 to about 5.0 weight
percent, basis the calcium hypochlorite, of solid wax binder
selected from the group consisting of microcrystalline hydrocarbon
wax and alkali metal salts of oxidized microcrystaline hydrocarbon
wax are described. The novel solid articles are provided in the
shape of, for example, tablets, which are prepared by dry blending
the granular calcium hypochlorite and wax binder and feeding the
mixture to a tableting press. The articles dissolve at a controlled
rate, depending on the amount of binder used, in water, thereby
providing a source of available chlorine over an extended period of
time.
Inventors: |
Iwanski; Donald P. (Allison
Park, PA) |
Assignee: |
PPG Industries, Inc.
(Pittsburgh, PA)
|
Family
ID: |
25093200 |
Appl.
No.: |
06/771,868 |
Filed: |
September 3, 1985 |
Current U.S.
Class: |
424/665;
252/187.24; 252/187.28; 252/187.27; 424/464 |
Current CPC
Class: |
C02F
1/76 (20130101); C01B 11/068 (20130101); C02F
1/688 (20130101); A01N 25/34 (20130101); A01N
59/00 (20130101); A01N 59/00 (20130101); A01N
2300/00 (20130101); C02F 2103/42 (20130101); C02F
2303/04 (20130101) |
Current International
Class: |
A01N
25/34 (20060101); A01N 59/00 (20060101); C01B
11/06 (20060101); C01B 11/00 (20060101); C02F
1/76 (20060101); C02F 1/68 (20060101); A01N
025/00 () |
Field of
Search: |
;424/149,78
;514/464 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Rose; Shep K.
Attorney, Agent or Firm: Stein; Irwin M.
Claims
What is claimed is:
1. A solid article comprising a compressed mixture of granular
calcium hypochlorite and from about 0.5 to about 5.0 weight percent
of a solid wax binder selected from the group consisting of
microcrystalline hydrocarbon wax and alkali metal salts of oxidized
microcrystalline hydrocarbon wax.
2. The article of claim 1 wherein the principal size distribution
of the granular calcium hypochlorite is between minus 6 and plus
100 U.S. Sieve.
3. The article of claim 2 wherein the binder is present in amounts
of from about 0.75 to 1.75 weight percent.
4. The article of claim 3 wherein the binder is the potassium salt
of oxidized microcrystalline hydrocarbon wax.
5. The article of claim 3 wherein the mass of the article is from
250 to 350 grams.
6. The article of claim 5 wherein the shape of the article is in
the form of a tablet having a diameter of from about 3 to about 3.5
inches.
7. The article of claim 1 wherein at least 10 weight percent of the
original mass of compressed calcium hypochlorite remains after 6
days of contact with water.
8. The article of claim 1 wherein the granular calcium hypochlorite
is at least 65 weight percent calcium hypochlorite.
9. The article of claim 2 wherein the principal size distribution
of the granular calcium hypochlorite is between minus 10 and plus
45 U.S. Sieve.
10. The article of claim 9 wherein the binder is present in amounts
of from 0.75 to 1.75 weight percent.
11. The article of claim 10 wherein the density of the article is
between about 1.6 and 2.3 grams per cubic centimeter.
12. The article of claim 10 wherein the principal size distribution
of the granular calcium hypochlorite is between minus 6 and plus 60
U.S. Sieve.
Description
DESCRIPTION OF THE INVENTION
The present invention relates to calcium hypochlorite compositions
and, more particularly, relates to a solid calcium hypochlorite
article, such as a tablet, which provides a continuous source of
available chlorine for disinfecting and sanitizing water supplies
over an extended period of time.
Calcium hypochlorite enjoys a major portion of the market for
available chlorine compounds, aside from chlorine itself, because
it is the cheapest and most stable solid composition known which
delivers all of its available chlorine immediately on contact with
oxidizable materials. Calcium hypochlorite compositions containing
at least 65 weight percent of calcium hypochlorite have been on the
market for many years and are used primarily as a commercial
bleaching and sanitizing agent, particularly in the disinfection
and sanitizing of water supplies such as swimming pool water. As a
source of available chlorine, calcium hypochlorite is a highly
soluble material which dissolves rapidly in water.
For the treatment of residential swimming pool water, it is
conventional to broadcast granular calcium hypochlorite
periodically directly on the water in the pool in quantities
sufficient to maintain the available chlorine at or above the
desired levels, e.g., from less than 1 part per million to a few
parts per million of chlorine. In an alternative method, tablets of
calcium hypochlorite are placed in the skimmer or in dissolving
baskets around the swimming pool to provide continuous contact
between the pool water and the solid calcium hypochlorite. A
further method used to treat swimming pool water is to add granular
or tabletted calcium hypochlorite to a dispensing device in which
the calcium hypochlorite is contacted with the water to be treated
so that dissolution of the calcium hypochlorite is controlled to
form a solution of the desired available chlorine concentration.
This concentrated solution is then added to the total body of pool
water to provide the desired available chlorine concentration.
When added to water at room temperatures, calcium hypochlorite
dissolves rapidly. Consequently, treatment of water, e.g., swimming
pool water, is required almost daily to maintain a disinfecting or
sanitizing quantity of available chlorine in the swimming pool. A
source of calcium hypochlorite which provides a relatively constant
source of available chlorine over a prolonged period, e.g., 4-6 or
7 days, is a highly desirable feature for the consumer and ultimate
user of calcium hypochlorite.
It has now been discovered that a compressed mixture of granular
calcium hypochlorite and from about 0.5 to about 5 weight percent,
basis the calcium hypochlorite, of a solid wax binder selected from
the group consisting of microcrystalline hydrocarbon wax and alkali
metal salts of oxidized microcrystalline hydrocarbon wax provides
an article which, when placed in contact with water, dissolves more
slowly than an article composed of binder-free compressed granular
calcium hypochlorite. When such articles are placed in the skimmer
or in a dissolving basket used at a swimming pool installation,
dissolution of the calcium hypochlorite in the article is prolonged
for from 4 to 6 days during which time the article provides a
source of available chlorine in amounts sufficiet for disinfecting
and sanitizing, i.e., a disinfecting amount.
DETAILED DESCRIPTION OF THE INVENTION
Granular calcium hypochlorite is commercially available and
generally contains from at least about 60 to about 70 percent by
weight of calcium hypochlorite. The remainder of the calcium
hypochlorite article of commerce is typically composed of varying
amounts of sodium chloride, calcium chloride, calcium hydroxide,
calcium chlorate and water. The aforementioned salts (other than
calcium hypochlorite) are incorporated into the commercial calcium
hypochlorite product during its synthesis and manufacture. Water
may comprise between about 2 and about 15 percent, e.g., between
about 4 and 10 percent of the calcium hypochlorite product.
In forming the article of the present invention, granular calcium
hypochlorite is blended with the binder material and compacted with
pressure into the shape desired, e.g., a tablet. The granular
calcium hypochlorite should be free-flowing to allow it to be
introduced into the compaction device, and such material may
exhibit a relatively broad particle size distribution. The latter
physical property permits the smaller particles to fill in the
spaces between the larger particles during compaction. It is
preferred that the particles comprising the granular calcium
hypochlorite be particulate rather than powdery in size since the
size of the particles compacted is believed to influence the rate
of dissolution of the compacted article.
As a general guideline, the particles may have a principal size
distribution between about minus 6 and plus 100 U.S. Sieve Series,
i.e., the particles vary in size principally between about 0.13
inches (3.3 millimeters) and about 0.006 inches (0.15 millimeters).
More commonly, the particles will have a principal size
distribution between about minus 6 and plus 60 U.S. Sieve.
Particularly suitable for use in producing articles of the present
invention is granular calcium hypochlorite having a size
distribution of minus 10, and plus 45 U.S. Sieve Series, i.e., the
granules are principally between about 0.08 and 0.014 inches (1.98
and 0.35 millimeters). Particles smaller than 60 U.S. Sieve present
in the granular calcium hypochlorite represent a minor percentage,
usually less than 2 percent, of the material charged to the
compaction device.
The binders used to agglomerate the granular calcium hypochlorite
in accordance with the present invention are microcrystalline
hydrocarbon waxes and alkali metal, e.g., sodium and potassium,
salts of oxidized microcrystalline hydrocarbon waxes.
Microcrystalline wax consists of high molecular weight saturated
aliphatic hydrocarbons, e.g., hydrocarbons containing about 48
carbon atoms. These waxes are available commercially and are
produced by deoiling and cutting petrolatums or pipe still bottoms.
The oxidized microcrystalline waxes are prepared by oxidizing the
microcrystalline wax with air in the presence of a catalyst such as
manganese or cobalt.
The wax binder is used in amounts of between about 0.5 and about
5.0 weight percent, basis the calcium hypochlorite. Typically, the
higher the amount of binder used within that range the longer is
the dissolution time for the calcium hypochlorite compositions of
the present invention. Hence, varying the amount of binder in said
compositions controls their rate of dissolution in water, such rate
being adjustable with the amount of binder used. For residential
swimming pools, binder levels of between about 0.5 and 2 weight
percent are useful. Such binder levels will provide dissolution
times of between about 4 and 6 or 7 days. Preferably between about
0.75 and about 1.75, e.g., 1.5, weight percent of the aforesaid wax
binder is used. The microcrystalline waxes used herein as binders
are available as finely-divided powders and are available
commercially as the Petrolite.RTM. series of microcrystalline
hydrocarbon and modified hydrocarbon waxes. These microcrystalline
waxes have a melting point of between about 95.degree. C. and
105.degree. C.
The articles of the present invention are prepared by dry blending
granular calcium hypochlorite and the solid wax binder in a
suitable blender and feeding the resulting mixture to conventional
size-enlargement equipment such as a molding press, tableting
press, roll-type press, pellet mill and screw extruder.
To assist in releasing the compressed calcium hypochlorite article
from the forming equipment, it may be convenient to incorporate a
small amount of lubricant (mold release agent) with the granular
calcium hypochlorite-microcrystalline hydrocarbon wax blend or to
dust the molds of the forming equipment with such agents. Typical
lubricants that may be used include metal salts of fatty acids,
e.g., fatty acids having at least 10 carbon atoms such as metal
salts of stearic acid. The cation of the metal salt should be
compatible with calcium hypochlorite, e.g., sodium, magnesium,
zinc, and calcium. The proportion of lubricant utilized may be
between about 0.1 and about 1.0 percent by weight.
The compressed article of the present invention may be prepared in
any convenient desired shape, e.g., a brick, briquette, triangle,
pellet, tablet, etc., depending upon the intended use of the
article. Preferably, the shape is that of a tablet. The compressed
article of the present invention may typically have a mass of
between about 250 and about 350, e.g., about 300, grams of which at
least about 94 percent, more typically at least 96.5 percent, is
the granular calcium hypochlorite. The compressed article may be of
a size which may be inserted readily into a skimmer or dissolving
basket used with swimming pools or dissolvers used to form
concentrated solutions of calcium hypochlorite. In the case of a
tablet, it is preferred that the diameter of such tablet be between
about 3 inches (7.6 centimeters) and about 3.5 inches (8.9
centimeters), e.g., between about 3.125-3.25 inches (7.9-8.3
centimeters), and be about 1 to 2 inches (2.5-5.1 centimeters),
e.g., 1.25 inches (3.2 centimeters) thick. The compacted article
preferably has a density of from about 1.6-2.3 grams per cubic
centimeter (g/cc), e.g., 1.8-2.2 g/cc, more preferably about 2
g/cc. Generally, the denser the compacted article, the slower the
dissolution of the article.
Solid articles of compressed granular calcium hypochlorite prepared
in accordance with the present invention will dissolve slowly over
a period of between about 4 and 6 or 7 days, depending on the
ultimate mass of the article and the amount of binder used, when
placed in a conventional skimmer used in association with swimming
pools and contacted with circulating pool water. The slow
dissolution of the aforesaid article thereby provides a source of
available chlorine for disinfecting and sanitizing the pool water
over the period of time required to dissolve substantially all of
the calcium hypochlorite in the article, e.g., a tablet. In a
preferred embodiment, the solid article is prepared in a manner
such that at least 10 weight percent of the original compressed
calcium hypochlorite will remain after about 6 days of such use.
More preferably, the calcium hypochlorite article provides a
relatively constant source of chlorine to the pool water so as to
maintain from about 1 to 2 parts per million of chlorine
therein.
The present invention is more particularly described in the
following examples which are intended as illustrative only since
numerous modifications and variations therein will be apparent to
those skilled in the art.
EXAMPLE 1
An eight quart V-blender was charged with 6.5 pounds of granular
calcium hypochlorite having a size distribution of minus 6 and plus
100 U.S. Sieve Screen size and about 65% available chlorine. The
desired level of additive was added to the calcium hypochlorite in
the blender and covered with a second 6.5 of the same granular
calcium hypochlorite. The blender was closed and ran for 45 minutes
to blend the ingredients. The blend was charged to a Stokes
R-tablet press having a die 2.5 inches (6.35 centimeters) in
diameter and 1 inch (2.54 centimeters) in depth and tablets
produced from the blend using a tableting pressure of 20 tons (18.1
metric tons). The additives and their amounts are listed in Table
I.
TABLE I ______________________________________ Tablet Wt., Additive
Amount, Wt. % Grams.sup.e ______________________________________ 1.
None 0 170 2. Calcium Stearate 1 -- 3. Calcium Stearate 2 -- 4.
Microcrystalline Wax.sup.a 1.5 184 5. Modified Microcrystalline
Wax.sup.b 1.5 177 6. Synthetic Clay.sup.c 2 -- 7. Calcium Carbonate
2 -- 8. Chlorinated Paraffin.sup.d 2 --
______________________________________ .sup.a Petrolite .RTM. X2010
.sup.b Petrolite .RTM. X5082 .sup.c Laponite .RTM. hectorite .sup.d
Chlorowax .RTM. 70 .sup.e Average of 10 Tablets
Dissolution rate of the tablets (except 2 and 3) was measured by
placing one tablet in a skimmer basket mounted in a plastic pail
through which water at room temperature (about 24.degree. C.) was
circulated from a 55 gallon (0.21 cubic meters) drum and monitoring
the available chlorine level in the circulating water.
The control tablet was exhausted in one day as were the calcium
carbonate, Chlorowax.RTM. 70, and Laponite.RTM. clay modified
tablets. The calcium stearate modified tablets were brittle and of
such poor quality with respect to physical integrity that their
dissolution rates were not measured. The microcrystalline wax
modified tablets had significantly slower dissolution rates--about
90 percent of the tablet being exhausted in about six days.
EXAMPLE 2
Calcium hypochlorite tablets modified with 1.5 weight percent
Petrolite.RTM. X-2010 microcrystalline wax and having a tablet
weight of about 292 grams were prepared from granular calcium
hypochlorite having a size distribution of minus 10 and plus 100
U.S. Sieve and about 65% available chlorine in accordance with the
procedure used in Example 1 except that a tableting pressure of 45
tons (40.7 metric tons) and a die having a diameter of 3.125 inches
(7.94 centimeters) and depth of 2 inches (5.1 centimeters) was
used. About 98 percent of the granular product was in the range of
minus 10 and plus 45 U.S. Sieve. The dissolution rate of such
tablets were tested by the technique described in Example 1. The pH
and temperature of the circulating solution for test A were
maintained at about 7.5 and 24.degree. C. respectively. For test B,
the pH and temperature were about 7.7 and 23.degree.-24.degree. C.
Results for two of such dissolution rate tests are tabulated in
Table II.
TABLE 2 ______________________________________ Test A Test B
Elapsed time, Ave. Avail. Elapsed time, Ave. Avail. Hours Chlorine,
ppm. Hours Chlorine, ppm. ______________________________________ 0
33.3 0 19.8 24.65 383.0 24.65 358.1 49.01 485.8 49.0 446.8 89.54
581.5 89.5 595.7 115.0 691.5 115.0 691.5 137.5 762.4 137.4 744.7
162.3 783.7 162.2 751.8 ______________________________________
The data of Tables I and II show that microcrystalline wax-modified
calcium hypochlorite tablets had significantly slower dissolution
rates than unmodified tablets and provided chlorine to the
circulating aqueous medium for from about 6 to 7 days, depending on
the total weight of the tablet.
Although the present process has been described with reference to
specific details of certain embodiments thereof, it is not intended
that such detail should be regarded as limitations upon the scope
of the invention except as and to the extent that they are inclined
in the acompanying claims.
* * * * *